While exploring Johns Pond Park in Mashpee a couple weeks ago, I noticed one pine tree that was covered in hardened sap blobs, each with a distinctive circular hole leading back into the tree’s trunk.  At the time I attributed the condition to a pest infestation, but had no way of identifying the specific pest. Thanks to some asking around and sharing the photos of the sap blobs with a professional entomologist, I now know that these “wounds” were caused by the larvae of the Zimmerman pine moth (Dioryctria zimmermani).

Infestations of the Zimmerman pine moth can be detected by the presence of sap or resin masses, covered with sawdust-sized crumbs (caterpillar excrement) near the entry holes.  The color and consistency of the resin masses will indicate whether the infestation is active or not; soft, white sap indicates an active larvae attack, while hard, dull masses indicate an old or inactive infestation.

Zimmerman pine moths overwinter as young caterpillars in shallow pits dug into the tree’s bark, becoming active with warmer weather around April where they will bore into various locations in the trunk to feed over the summer.  Although this feeding typically occurs near the top of the tree in younger pines, active feeding is more common lower on the trunk in older trees, which was the case for the tree I encountered. In early August, the moths emerge as adults and lay eggs on the trunk of the tree. When the eggs hatch as young caterpillars, they feed on bits of bark until they create a shallow pit in which to rest for the winter and the whole cycle starts again.

Although the adult moth is small, with a gray body and a wingspan between 1 and 1-1/2 inches, it is actually the largest of the pine boring moths. The fore-wings are mottled with zig-zag lines of red and gray, while the hind wings light tan, becoming darker near the edges. This coloration provides excellent camouflage while the moth is resting on a pine trunk, making them very difficult to find since they are nocturnal and are inactive during the day. Photo below from the Purdue Extension Zimmerman Moth Fact Sheet.